1. Field of the Invention
The present invention relates to a liquid crystalline di(meth)acrylate compound, a phase difference film, an optical film, a polarizing plate, a liquid crystal panel and a liquid crystal display device.
2. Description of the Related Art
A phase difference film is an optical film used for converting linearly polarized light into circularly polarized light or elliptically polarized light, or conversely converting circularly polarized light or elliptically polarized light into linearly polarized light. As a phase difference film, phase difference films obtained by stretching a polymer film such as polycarbonate and polystyrene have been previously used.
However, since the polymer film has usually a thickness of about 40 to 100 μm, for example, when the film is applied to a liquid crystal display device, thinning of which is desired, a thinner phase difference film is desired.
Then, as a substitute for the stretched polymer film, a phase difference film using a liquid crystal monomer is paid an attention (for example, see Macromolecules, 1995, 28, 3313-3327). Usually, a retardation value of a phase difference film is determined by a product of a birefringence index (Δn) and a thickness, but since a liquid crystal monomer has great Δn, the liquid crystal monomer has an advantage, when one intends to obtain a prescribed retardation value, a thickness of a phase difference film can be advantageously reduced.
As the aforementioned phase difference film, for example, an optical film obtained by coating a mixed solution containing a liquid crystal monomer on a substrate, orienting this uniformly, and irradiating with ultraviolet-ray to cure it has been proposed (for example, see Japanese Patent Application Laid-Open (JP-A) No. 8-283718). Examples of property that the liquid crystal monomer is required to have when such the optical film is used as a phase difference film include not only excellent transparency of a cured film, but also better solubility in a solvent, uniform orientation of the liquid crystal monomer, better crosslinking property (curability) with ultraviolet-ray, and uniform fixation of the orientation state.
However, since the previous liquid crystal monomer has Δn greater than 0.10, when one tries to manufacture a phase difference film having a small retardation value using the liquid crystal monomer, a designed value of a thickness of a film is usually extremely small as about 1 μm, and it is extremely difficult to control a thickness. In addition, there is a problem that a small variation in a thickness manifests a great variation in a retardation value, and this deteriorates display uniformity of a liquid crystal display device.
In particular, in recent years, enlargement and high functionalization of a liquid crystal monitor, a liquid crystal television and the like have been rapidly progressed and, in various optical films such as a polarizing plate and a phase difference film used in them, further improvement in property and further improvement in quality are desired. Under such the circumstances, as the aforementioned liquid crystal monomer, development of a phase difference film using a liquid crystal monomer exhibiting further smaller Δn (e.g. 0.10 or smaller) than usual has been desired.